There are a number of turn indicator switches one of which is shown in FIGS. 8 through 12.
FIG. 8 is an exploded view of major parts of a turn indicator switch in which reference numeral 1 refers to a case mounted on a steering cover (not shown), 2 to a switch activating member mounted in a chamber 1a defined by the case 1, 3 to an operating lever connected to the switch activating member 2 and exposed through the case 1, and 4 to a cover closing the chamber 1a and fixed to the case 1. The switch activating member 2 has on an upper surface thereof a beveled cam 5 and offset recesses 6. The switch activating member 2 is also provided along its outer vertical walls with two blind bores 7, of which only one is illustrated. Reference numeral 8 designates a cam plate engaging the offset recesses 6 and movable therein back and forth. The cam plate 8 is biased in its advancing direction by a pair of springs 9 having a relatively large resiliency, and is reliably held in the offset recesses 6 by a pair of stopper plates 10 fixed to the switch activating member 2 by screws. Reference numeral 11 denotes a drive member slidably engaging the blind bores 7 and biased outwardly by springs 12.
The case 1 has a cam surface inwardly projecting from its inner wall surface to guide slidably movements of the drive member 11 therealong. Reference numeral 14 denotes a cam member having a pair of projections 14a on the upper surface thereof and having an engaging pin 14b on the bottom surface thereof. The cam member 14 is biased forwardly by a spring 15 having both ends fixed to the cover 4. The projections 14a of the cam member 14 are accepted in arcuate guide holes 4a formed in the cover 4. The engaging pin 14b of the cam member 14 contacts tapered cam surfaces of the beveled cam 5.
FIGS. 9 through 12 are plan views illustrating the turn indicator switch mounted on a steering assembly. In these drawings, reference numeral 16 refers to a steering shaft, and 17 to a cancelling cam co-rotatable with the steering shaft 16 and having two projections 17a at 180 degrees interval.
As shown in FIG. 9, when the operating lever 3 takes its neutral position, the engaging pin 14b of the cam member 14 engages the summit of the triangle cam 5 to maintain the cam member 14 at its retracted position outside the rotation orbit of the projections 17a of the cancelling cam 17 against the energy of the spring 15. Therefore, regardless of rotation of a steering wheel (not shown), the projections 17a of the cancelling-cam never contact the cam member 14, and the switch activating member 2 and the operating lever 3 are maintained at their neutral positions.
Referring to FIG. 10, when the operating lever 3 is rotated in a direction shown by arrow A, for example, from the neutral position, upper one of the drive members 11, hereinafter designated by 11a whereas the lower drive member is denoted by 11b, moves beyond a ridgeline of the cam surface 13. Therefore, the switch activating member 2 and the operating lever 3 are locked there, and a left-turn or right-turn switch (not shown) is activated. This rotation of the switch activating member 2 changes the positional relationship between the triangle cam 5 and the cam plate 14. Therefore, the spring 15 in FIG. 8 biases the cam plate 14 to move the engaging pin 14b away from the summit of the stopper cam 5 along one of side slopes thereof. Therefore, the cam plate 14 projects through the case 1 into the orbit of the projections 17a.
Referring to FIG. 11, when the steering wheel is rotated back to its original position in a direction shown by arrow B in the drawing, the cam member 14 in its projecting position contacts one of the projections 17a of the cancelling cam 17 during the return movement of the steering wheel. Due to this, the cam member 14 rotates in arrow C direction about the lower one of the projections 14a in the drawing and urges one end portion of the cam plate 8. Since the cam plate 8 is connected to the switch activating member 2 via the springs 9 having a relatively large energy, the cam plate 8, switch activating member 2 and operating lever 3 rotate together clockwisely in the drawing to their neutral positions. This is just the cancelling motion.
On the other hand, when a driver commences a returning rotation of the steering wheel from the configuration of FIG. 9 while holding the operating lever 3 in order to continue a turn indicating flashing after a return motion of the steering wheel to its neutral position due to a caster effect, the cam member 14 contacts one of the projections 17a of the cancelling cam 17 in the same returning motion, and rotates in arrow C direction. In this case, since the operating lever 3 and the switch activating member 2 are fixed by the driver, the energy applied from the cam member 14 to the cam plate 8 is absorbed by contraction of the lower spring 9 in the drawing, and no power for cancelling operation is transmitted to the operating lever 3. When the cancelling cam 17 further rotates in arrow B direction in FIG. 12 until the steering wheel reaches its neutral position, the projection 17a of the cancelling cam 17 moves apart from the cam member 14, and the operating lever 3 is maintained in the locked condition of FIG. 10 also after the driver removes his hand from the operating lever 3.
As explained above, turn indicator switches in general include a cancelling mechanism to automatically return an operating lever from a locked position to its neutral position upon a return movement of a steering wheel. This cancelling mechanism requires a safety function to establish engagement or disengagement between the cam member 14 and the cancelling cam 17 while fixing the operating lever 3 at its locked condition.
In this connection, the prior art employ relatively stubborn springs 9 to connect the cam plate 8 to the switch activating member 2. However, it is very difficult to make the energy of the springs 9 uniform, and prior art cancelling mechanisms often invite a malfunction caused by uneven strengths of the springs 9 in their cancelling action. More specifically, if the springs 9 are stubborn, they cannot sufficiently absorb the energy of the cam member 14 applied to the cam plate 8, and the resetting force is applied to the cam plate 8 and the cam member 14, and often destroys them. On the other hand, if the springs 9 are weak, they also contract upon a cancelling operation, and cannot transmit the energy of the cam member 14 to the switch activating member 2. This invites unreliable cancelling motion of the system.
Beside this, the prior art cancelling mechanism requiring the springs 9 is expensive due to a larger number of parts or members, and requires an increased effort in its assembling process to forcibly contract the stubborn springs 9 to insert them between the cam plate 8 and the switch activating member 2.